A conveyor system using self-propelled carriers has advantages over conveyors in which the carriers are advanced by chains which travel along parallel to the rails, particularly in that the propelling means is compact and the conveyor system is simplified.
Conventional self-propelled carriers are disclosed, for example, in Japanese Laid-Open Patent Application No. 186756/1984 and Japanese Laid-Open Utility Model Application No. 24362/1986. In Application No. 186756/1984, running rails are provided by skirt-like support members suspended in opposed spaced relation from both sides of a support stand projecting upwardly from the floor. The carrier rides over the support members and has depending skirt portions embracing the outer sides of the support members and at the bottom of the skirt portions have means extending inwardly and mounting wheels which roll on the running rails. The propelling device is mounted between the running rails and has shoes or other collectors adapted to ride on a bus bar extending between the running rails. The bus bars are therefore enclosed between the running rails and are covered by the supporting members for the running rails, and the collector which engages the bus bars is also covered by these elements and also the upper part of the carrier. This not only results in inconvenience in maintenance of the drive means but also the presence of the support stands in the space between the rails requires that one running rail be mounted on an axle separate from the axle mounting the wheel which supports the carrier on the other running rail. Since the axles for the right and left wheels are on opposite sides of the carrier, only one axle may be driven by the propelling device and the other wheel or wheels are rotated by the travel of the carrier on the rail. Since the carrier is driven on one of the rails and not the other, a torsional moment is applied to the carrier which may impede the running of the carrier on the rails. Furthermore, since the running rails are mounted on the inside of the lower end of the rail support members which are suspended in a skirt-like fashion, an inward bending moment due to the load of the carrier is applied to the rail support members which requires strengthening of the mounting construction of the support members and which renders adjustment of the spacing between the rails difficult.
In Application No. 24362/1986, the running rails are mounted on the top of the support stands, but the disclosed apparatus drives the carrier by means of a single wheel engaged on one of the tracks, the carrier having guide rollers engageable with the other of the tracks for positioning purposes. Therefore, the device of this application is subject to the same deficiency with respect to torsional moment as the device of Application No. 186756/1984. Furthermore, the arrangement of the carrier on the running rails of Application No. 24362/1986, exposes the running surfaces of the rails except when the carrier travels over them and covers them. As a result, foreign matter may adhere to and accumulate on the running surfaces which may cause slippage of the drive wheel on the rail during propusion of the carrier, rendering positive driving of the carrier difficult. Thus, when the carrier is used in an assembly line for automobiles, the assembling work may be inconveniently delayed.
Furthermore, the rails are mounted on sides of the support stands to enable the running wheel and an anti-float roller to engage on the top and bottom respectively of the rail, there is a further disadvantage in restricting the adjustment of the spacing between the rails, as in the previously mentioned U/M application.
If the running rails are made of channel members, and the wheels are arranged to ride on the lower flange, the upper flange protects the running surface from dropping and adhesion thereon of foreign matter, dust or the like. However, when the rails are along a curved path, or the rails must include a switch or change in direction, the travel of the wheels becomes irregular or else the switching arrangement unduly complicates the construction of the rail. Therefore, it is the practice to cause the wheels to travel on the upwardly-facing surface of the running rail.
It has been suggested that cover elements may be provided which overlie the running surfaces of the rail, but such cover elements provide an obstacle to the installation of the conveyor, both in mounting the conveyor in the factory and in assembling the carriers with the conveyor. Accordingly, the cover elements must be removed during installation and reinstalled, entailing substantial additional labor.
With the foregoing in mind, it is clear that the prior art self-propelled conveyors for conveying articles do not permit the use of a common drive axle for wheels on opposite rails and render the adjustment of the rail spacing difficult. Where the carrier running system is enclosed, the maintenance of the system is difficult and when it is exposed, the likelihood of slippage renders the system unsatisfactory.